A study on the measurements of residual stresses at the interfaces of aluminum-graphite composites and silicon film on quartz

In order to quantitatively determine the residual stresses at the interfaces of composite materials measurements using by the laser Raman microprobe for laminate composites, and x-ray diffraction for graphite fiber reinforced aluminum metal matrix composite have been performed. For the Raman microprobe method, the Raman band shift due to applied stress was calibrated using strain gauges on quartz plates. A model involving exponential strain gradient in the substrate and no strain gradient in the film was developed. The measurements of residual strains at the silicon/quartz interfaces using the Raman microprobe were compared to expected residual strains by the model. The model shows that a small volume of substrate near the interface about 2 times the film thickness was affected by the thermal mismatch of the two regions.; Approximately 5-10 times higher residual strains were expected at the substrate side of the interfaces compared to the measured results. This is explained by the focused beam Raman experiments averaging along the probe thickness of about 10 {dollar}mu{dollar}m resolution. The recrystallization process of silicon film by thermal annealing was also investigated using Raman spectroscopy. For aluminum film on quartz tensile residual stresses were subsequently observed at the interfaces of the quartz plates with aluminum-aluminum oxide.; Lower residual stresses of the pitch-based graphite fiber reinforced aluminum matrix composites were measured by x-ray diffraction when compared to the calculated values. This fact was explained by the stress relaxation in the fiber as well as in the matrix. The displacements within the graphite fiber relative to the interface between the graphite fiber and aluminum matrix during thermal cycling were monitored by in-situ SEM experiments. The lower shear strength of the basal plane in the highly graphitized high modulus fiber explains the displacement within the fiber and the relaxation of the theoretically expected high residual stresses. These shear strains within the fiber are then related to measured residual stresses and to the impact on the composite coefficient of thermal expansion and potential damage under thermal fatigue loading.